How to Bleed a Steam Boiler System

Bleed the air out of your steam-heat system to improve its performance.

If you have a hot-water boiler system in your home, you may need to bleed the system so it performs at its optimal level. When you bleed the system, you are eliminating small pockets of air trapped in the pipes, which prevent the water from circulating quickly through the system. Sometimes you only have to bleed a radiator in one room, while other times you have to bleed the whole system. It's recommended that you bleed the air out of the boiler system before cold weather arrives. This entire process should take less than 30 minutes.

Things You'll Need

• Needle-nose pliers
• Small plastic bowl

Instructions

1. Turn on the steam boiler system manually by turning up the temperature until the furnace turns on.

2. Loosen the bleeder valve on one of the radiators, using a pair of needle-nose pliers or a radiator key.

3. Drain the air from the system. Listen for a hissing sound as you open the valves and the trapped air begins to escape. Hold a small plastic bowl underneath the bleeder valve to catch any drips. As soon as the hissing stops and only water comes out, you have bled that radiator.

4. Drain the air from each radiator in the system. Start with the highest rooms in your home if you have multiple stories. These high radiators will contain the most trapped air.

5. Test the system. Traveling from room to room while the boiler system is still running, put your hand on each radiator and check for warmth. If the entire radiator feels warm, then most of the air is expelled. If the radiator is cold, you have to bleed it again.

Tips & Warnings

• If after repeatedly bleeding the air from the system you still have a cold radiator, you may have a larger problem and should consult with a plumber.

References

• The Family Handyman: How to Bleed a Hot Water Radiator and Clear a Steam Radiator Vent